should be placed with Polycentrus side by side with the Chromides and Helichthyoids. The manner in which Pterophyllum moves is quite peculiar. The profile of the head and the extended anterior margin of the high dorsal are brought on a level, parallel to the surface of the water, when the long ventrals and high anal hang down vertically, and the fish progresses slowly by the lateral beating of the tail.—L. A. Footnote 54: ON THE XINGU, August 23d, 1865. MY DEAR FRIEND:—I am worn out with fatigue, but I will not go to rest before writing you a word. Yesterday evening we obtained twenty-seven species of fish at Gurupá and this morning fifty-seven at Porto do Moz,—eighty-four species in all, in less than twelve hours, and of this number fifty-one are new. It is wonderful. I can no longer put in order what is brought to me as fast as it arrives, and as to obtaining colored drawings of all, it is no longer possible, unless we pass a whole week here on our return. Wholly yours, L. AGASSIZ. Footnote 55: Representations of these hills may be found in the Atlas of Martius and in Bates’s “Naturalist on the Amazons.” Footnote 56: Afterwards I made a longer stay at Monte Alégre, and learned to know its picturesque nooks and dells, where a luxuriant vegetation is watered by delicious springs. I feel that the above description is superficial; but I let it remain, as perfectly true to my first impressions. Footnote 57: I soon became convinced after leaving Pará that the faunæ of our different stations were not repetitions of each other. On the contrary, at Breves, Tajapurú, Gurupá,—in short, at each stopping-place, as has been seen,—we found another set of inhabitants in the river, if not wholly different from the last, at least presenting so many new species that the combination was no longer the same. It became at once very important to ascertain whether these differences were permanent and stationary, or were, in part at least, an effect of migration. I therefore determined to distribute our forces in such a way as to keep collecting parties at distant points, and to repeat collections from the same localities at different seasons. I pursued this method of investigation during our whole stay in the Amazons, dividing the party for the first time at Santarem, where Messrs. Dexter, James, and Talisman separated from us to ascend the Tapajoz, while Mr. Bourget remained at Santarem, and I, with the rest of my companions, kept on to Obydos and Villa Bella.—L. A. Footnote 58: